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Support variable expansion in DotEnv features #65705
Description
What is the problem this feature will solve?
Sometimes it's helpful to derive the value of variables from other variables, using variable expansion.
For example, consider the following .env file:
APPLICATION_PORT: 8080
BASE_URL: http://localhost:8080The APPLICATION_PORT and BASE_URL should have the same port. For reasons external to this issue, BASE_URL cannot be split into two variables without causing confusion.
If there are external overrides to APPLICATION_PORT, they won't remain in sync with BASE_URL.
What is the feature you are proposing to solve the problem?
Instead we could write .env files like this:
APPLICATION_PORT: 8080
BASE_URL: http://localhost:${APPLICATION_PORT}This is already supported by at least bash, and the concept of variable expansion in environmental configuration is also common in ecosystems such as Kubernetes.
What alternatives have you considered?
- Using
dotenvx - Splitting variables up into their lowest common set
Activity
Shivang9983 commentedon Sep 5, 2026
Hi, @daeyeon I’d like to work on this issue.
I’d like to investigate adding variable expansion support to Node.js DotEnv handling, including references such as
${APPLICATION_PORT}inside another variable's value.I can look into the existing DotEnv parser and determine how expansion should interact with variable ordering, environment overrides, undefined references, and recursive/circular references while keeping the current behavior backward compatible.
I’ll also add appropriate tests covering the supported expansion syntax and relevant edge cases.
If this issue is available, please assign it to me. Thanks!
avivkeller commentedon Sep 23, 2026
cc @nodejs/security-wg Wouldn't this have security implications, e.g. if you set one variable to a user-controlled value, they can affectively access and modify any system variable?
For example,
Allowing bash expansion allows for the modification of variables outside the dotenv file, no?